PROJECT SUMMARY Transmembrane proteins play critically important roles in human physiology and disease. Among the many roles of such transmembrane proteins is the regulation of serum iron concentration. Iron levels must be maintained at sufficient levels to support erythropoiesis; failure to do so results in iron deficiency anemia. Conversely, iron overload secondary to the inherited diseases of hemochromatosis results in liver cirrhosis, diabetes, and cardiomyopathy. Serum iron levels are tightly controlled by the protein hormone hepcidin, which induces degradation of the iron efflux transporter ferroportin and thereby prevents uptake of iron from enterocytes and recycling of iron from macrophages. However, the molecular basis of ferroportin function and its regulation by hepcidin remains poorly characterized. The proposed research will elucidate the biochemical, structural, and biophysical basis of ferroportin activity and will develop new ways of modulating ferroportin function. These studies will develop novel strategies for treating diseases resulting from dysregulation of iron homeostasis. More broadly, elucidating the molecular basis of ferroportin function will yield general insights into the Major Facilitator Superfamily of transporters, a large group of transmembrane proteins responsible for many disease states.